Need help installing a new tub/shower faucet.

I need some advice for installing a new tub/shower valve. The first two photos show the existing arrangement, and the last photo shows the new valve. I want to use galvanized pipe and fittings since Iâ€™m not capable of doing copper.
1. The new valve has male (IPS) threads sticking out of it instead of female threads (like the old one). I would like to use Â½â€ couplings (female/female) to on each of male threads of the valve then re-attach everything like the old valve was installed. Is that a good way to do this?
3. Are the male IPS threads compatible with the female NPT (I think) coupler threads?
4. Should I add more unions?
5. How do I calculate the new lengths that will be needed on the left and right side of the valve?
Thanks, Wayne